There have been known methods for producing cyclic ethers; for example, a method of producing 2,5-dihydrofuran through dehydration-cyclization of cis-2-butene-1,4-diol in the presence of a hydrogensulfate salt or in the presence of sulfuric acid and a base (see Patent Document 1); a method of producing 2,5-dihydrofuran including causing vaporized cis-2-butene-1,4-diol to pass through an alumina-catalyst-containing tube with helium and hydrogen (see Non-Patent Document 1); a method of continuously producing 2,5-dihydrofuran through feeding cis-2-butene-1,4-diol to a reactor in the presence of an aluminum oxide catalyst for subjecting the diol to dehydration-cyclization reaction at ambient pressure and 170 to 220° C. (see Patent Document 2); and a method of producing a cyclic ether including subjecting a saturated α,ω-diol to dehydration-cyclization reaction in the presence of an aluminum oxide which has received a specific treatment (see Patent Document 3).    Non-Patent Document 1:Industrial Eng. Chem. Product Res.& Dev., 1973, Vol. 12, No. 3, p. 184-189    Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 1997-110850    Patent Document 2: German Patent No. 1,211,219    Patent Document 3: Japanese Patent Application Laid-Open (kokai) No. 1981-73080